title: AID induces double-strand breaks at immunoglobulin switch regions and c-MYC causing chromosomal translocations in yeast THO mutants.
abstract: Transcription of the switch (S) regions of immunoglobulin genes in B cells generates stable R-loops that are targeted by Activation Induced Cytidine Deaminase (AID), triggering class switch recombination (CSR), as well as translocations with c-MYC responsible for Burkitt's lymphomas. In Saccharomyces cerevisiae, stable R-loops are formed co-transcriptionally in mutants of THO, a conserved nuclear complex involved in mRNP biogenesis. Such R-loops trigger genome instability and facilitate deamination by human AID. To understand the mechanisms that generate genome instability mediated by mRNP biogenesis impairment and by AID, we devised a yeast chromosomal system based on different segments of mammalian S regions and c-MYC for the analysis of chromosomal rearrangements in both wild-type and THO mutants. We demonstrate that AID acts in yeast at heterologous S and c-MYC transcribed sequences leading to double-strand breaks (DSBs) which in turn cause chromosomal translocations via Non-Homologous End Joining (NHEJ). AID-induced translocations were strongly enhanced in yeast THO null mutants, consistent with the idea that AID-mediated DSBs depend on R-loop formation. Our study not only provides new clues to understand the role of mRNP biogenesis in preventing genome rearrangements and the mechanism of AID-mediated genome instability, but also shows that, once uracil residues are produced by AID-mediated deamination, these are processed into DSBs and chromosomal rearrangements by the general and conserved DNA repair functions present from yeast to human cells.
authors.affiliation: Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Universidad de Sevilla-CSIC, Sevilla, Spain.
authors.forename: José F
authors.initials: JF
authors.lastname: Ruiz
authors.forename: Belén
authors.initials: B
authors.lastname: Gómez-González
authors.forename: Andrés
authors.initials: A
authors.lastname: Aguilera
mesh_terms: D000818:Animals; D001483:Base Sequence; D015825:Chromosomes, Fungal; D003564:Cytidine Deaminase / Q000235:genetics / Q000378:metabolism*; D053903:DNA Breaks, Double-Stranded; D006801:Humans; D007134:Immunoglobulin Switch Region; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D016415:Sequence Alignment; D014178:Translocation, Genetic; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D016271:Proto-Oncogene Proteins c-myc; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase